(1) Field of the Invention
This invention is related to the developing of a selectively exposed layer of resist formed on an integrated circuit wafer and more particularly to stopping the developing process and removing the resist using immersion in de-ionized water followed by a vacuum dry period. The vacuum dry period may also include heating the wafer using a heat lamp.
(2) Description of the Related Art
U.S. Pat. No. 4,902,608 to Lamb et al. and U.S. Pat. No. 5,025,280 to Lamb et al. describes a method and apparatus for immersing a selectively exposed layer of photoresist on a wafer first in a bath of developer and next in a bath of de-ionized water. While the wafer is in the de-ionized water it is slowly turned in the water. The wafer is then removed from the water and rapidly spun to spin dry the wafer and photoresist.
U.S. Pat. No. 4,982,215 to Matsuoka describes a developing process where a workpiece having a resist layer is immersed in a bath of developer at a first temperature. Electrical current between the workpiece and an electrode also immersed in the developer to monitor the progress of the developing process. When the developing process has been completed an additional amount of developer at a second temperature, lower than the first temperature, is added to the original developer as the withdrawl of the developer is begun. The progress of the development is thus retarded providing precision for the endpoint of the development process.
This invention describes a method and apparatus for developing a resist pattern that does not require spinning the wafer and does not require batches of developer at different temperatures.
Resist patterns are routinely used in the manufacture of integrated circuit wafers. These resist patterns are formed by selectively exposing a layer of resist, using photolithography or electron beam methods or the like, and developing the selectively exposed layer of resist to form the pattern. Developing the resist is carried out by placing the exposed resist in contact with liquid developer material for a certain time followed by washing the developer away with de-ionized water, or other cleaning liquid. The de-ionized water is then removed by drying the resist pattern.
As the level of integration of integrated circuits increases problems are encountered with the conventional method of developing resist patterns. Some of the problems encountered developing resist patterns will be described with reference to FIGS. 1-3. FIG. 1 shows the top view of an integrated circuit wafer with a layer of selectively exposed resist formed thereon and liquid developer material placed on the layer of selectively exposed resist 10. FIG. 2 shows a cross section view of the integrated circuit wafer of along the line 2-2xe2x80x2 of FIG. 1. FIG. 2 shows the integrated circuit wafer 12 placed on a wafer holder 18. The layer of selectively exposed resist 14 is formed on the integrated circuit wafer 12. Liquid developer material 16 is placed on the layer of resist 14. The wafer holder 18 is attached to a shaft 20.
FIG. 3 shows a cross section view of the integrated circuit wafer after the developing of the exposed resist has been completed. The layer of resist has been developed forming a resist pattern 15. The shaft 20 attached to the wafer holder 18 is attached to a means 22 for spinning the shaft 20, wafer holder 18, integrated circuit wafer 12, and developed resist pattern 15 as indicated by the rotational arrow 36. As the spinning of the wafer begins, and is still at a low speed, valves 27 and 29 are opened and de-ionized water is fed from a de-ionized water supply 26 through a pipe 28 to nozzles 30 which spray de-ionized water on the developed resist pattern 15 forming a layer of deionized water 24 over the resist pattern. De-ionized water is also directed from the de-ionized water supply 26 through a pipe 32 to a nozzle 34 to spray de-ionized water on the back side of the wafer. The valves 27 and 29 are then closed stopping the supply of de-ionized water to the integrated circuit wafer. The wafer is then spun at high speed to dry the wafer, thereby removing any residual de-ionized water. In this conventional developing method the de-ionized water, or other cleaning liquid, imparts a force to the fine elements of the resist pattern as the wafer is spun at high speeds often damaging the resist pattern.
It is a principle objective of this invention to provide a method of developing and cleaning a layer of selectively exposed resist which will avoid damage to the developed resist pattern.
It is another principle objective of this invention to provide an apparatus for developing and cleaning a layer of selectively exposed resist which will avoid damage to the developed resist pattern.
These objectives are achieved by immersing the integrated circuit wafer with developer on the resist pattern in de-ionized water after developing the resist pattern has been completed. There is no spinning of the wafer however low levels of ultrasonic power may be used. The wafer is then removed from the de-ionized water and the chamber containing the wafer is evacuated, using a means such as a vacuum pump, to dry the wafer. Heat, using a means such as a heating lamp, may be applied to the wafer while the chamber is evacuated. During the developing process no force is exerted on the resist pattern by the cleaning liquid, damage to the pattern is avoided, and a wider choice of resists is available.